i have been reading old information about mahachai bettas being brackish water dwelling bettas.

for this discussion and purpouses brackish water is defined as a mix of salt and sea water with an sg of more than 1.005 and less than full sea water.

i have not found any indication that the mahachai bettas is not brackish tollerant but information is not easy for me to find that is recent mostly they are 3 - 5 years old and talking about the "new betta speicies"

I'm not 100% sure but I believe most betta species can tolerate a rather salty water (not sea water). Since all of them have been kept in fresh water, it would be safer to acclimate very slowly - like over 1 week.

Most of our members, including myself, do not specialize in wilds and don't really have much information to offer you. I suggest checking with the IBC website and forum for wild type-related information. They should have the most abundance and accuracy of information. From what I've heard though, I do believe they're a brackish fish.